Extrusion of graphite bodies

Abstract

A method of forming graphitic bodies comprises the steps of:— a) forming under high shear a mouldable composition comprising:— i) graphite powder; ii) a binder; and iii) a fluid carrier b) working under high shear said mouldable composition to form an extruded shape; c) forming bodies from said shape; and d) heat treating said bodies to stabilise the structure. In which either the fluid carrier is an aqueous fluid carrier, and/or the bodies are impregnated to close porosity and/or the bodies are machined to form structures in their surface.

1 . A method of forming graphitic bodies comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         2 . The method of  claim 1 , in which, after heat treatment, the bodies are machined to form features in their surfaces.  
     
     
         3 . The method of  claim 1 , in which before heat treatment, the bodies are machined to form features in their surfaces.  
     
     
         4 . The method of any one of claims  1 ,  2 , or  3 , in which the bodies are impregnated to close porosity in the bodies.  
     
     
         5 . The method of any one of  claims 1  to  4 , in which the binder comprises a polyvinyl alcohol.  
     
     
         6 . The method of any one of  claims 1  to  4 , in which the binder comprises a lignosulphonate.  
     
     
         7 . The method of any one of  claims 1  to  4 , in which the binder comprises a polyvinyl alcohol and a lignosulphonate.  
     
     
         8 . The method of any one of  claims 1  to  7 , in which the bodies are graphitic sheets.  
     
     
         9 . The method of any one of  claims 1  to  8 , in which the step of working the mouldable composition comprises extrusion through an aperture having at least one dimension less than 4 mm.  
     
     
         10 . The method of  claim 9 , in which the step of working the mouldable composition comprises extension through an aperture having at least one dimension less than 3.5 mm  
     
     
         11 . The method of  claim 10 , in which the step of working the mouldable composition comprises extrusion through an aperture having at least one dimension less than 2.5 mm  
     
     
         12 . The method of  claim 11 , in which the step of working the mouldable composition comprises extrusion through an aperture having at least one dimension less than 1.5 mm.  
     
     
         13 . The method of any one of  claims 1  to  12 , in which the body is in the form of a plate.  
     
     
         14 . The method of any of  claims 1  to  12 , in which the shape is produced in the form of a tube.  
     
     
         15 . The method of  claim 14 , in which the tube is split lengthwise and flattened to form a sheet.  
     
     
         16 . The method of any one of  claims 1  to  15 , in which the body is rolled to form a sheet of specified thickness.  
     
     
         17 . The method of any one of  claims 1  to  16 , in which features are formed in the bodies in a rolling process.  
     
     
         18 . The method of any one of  claims 1  to  16 , in which features are formed in the bodies in a die stamping process.  
     
     
         19 . The method of any one of  claims 1  to  18 , in which a mesh of metal or plastics is pressed into the graphitic material to form a composite body.  
     
     
         20 . The method of any one of  claims 1  to  19 , in which the mouldable composition comprises a plasticiser.  
     
     
         21 . The method of  claim 20 , in which the mouldable composition comprises a plasticiser which is also a binder.  
     
     
         22 . The method of  claim 20  or  claim 21 , in which the plasticiser is a lignosulphonate.  
     
     
         23 . The method of any one of  claims 1  to  21 , in which the binder is mixed with the graphite powder as dry ingredients prior to mixing with the fluid carrier.  
     
     
         24 . The method of any one of  claims 1  to  23 , in which a dispersant is used to prevent aggregation of the binder.  
     
     
         25 . The method of any one of  claims 1  to  24 , in which the mouldable composition is de-aired prior to worlding the mouldable composition under high shear to form the extruded shape.  
     
     
         26 . The method of any one of  claims 1  to  25 , in which the mouldable composition comprises a filler.  
     
     
         27 . The method of  claim 26 , in which the filler comprises a carbonaceous filler.  
     
     
         28 . The method of any one of  claims 1  to  27 , in which the amount of graphite expressed as a dry weight percentage of the mouldable composition is in excess of 30%.  
     
     
         29 . The method of  claim 28 , in which the amount of graphite expressed as a dry weight percentage of the mouldable composition is in excess of 60%.  
     
     
         30 . the method of  claim 29 , in which the amount of graphite expressed as a dry weight percentage of the mouldable composition is in excess of 80%.  
     
     
         31 . The method of  claim 30 , in which the mouldable composition comprises in weight percent (as a proportion of the components excluding the fluid carrier):—
 Graphite 80-90%  
 Binder 10-20%  
 Plasticiser 0-10%.  
 to which a fluid carrier in amounts in the range 10-40% by weight of the total of said components is added in mixing.  
 
     
     
         32 . The method of  claim 31 , in which the amount of fluid carrier is in the range 15-35%.  
     
     
         33 . A mouldable composition, as described in any one of  claims 1  to  32 , housed in a container to prevent loss of fluid during storage.  
     
     
         34 . A mouldable composition, as claimed in  claim 33 , in which the composition is in the form of a pliable sheet  
     
     
         35 . Use of a mouldable composition, as claimed in  claim 33  or  claim 34 , as a mouldable graphitic material that can be formed to shape and air dried to set  
     
     
         36 . A graphitic component for a fuel cell, formed by a method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder,  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) worlding said mouldable composition under high shear to form an extruded shape;  
 c) forming the graphitic component from said shape;  
 d) heat treating said graphitic component to stabilise the structure.  
 
     
     
         37 . A graphitic component, as claimed in  claim 36 , comprising flow fields formed in the graphitic component either before or after heat treating said graphitic component.  
     
     
         38 . A graphitic component, as claimed in  claim 36  or  37 , in which an impregnated material closes porosity in the graphitic component.  
     
     
         39 . A bipolar plate for a fuel cell, comprising a graphitic component as claimed in any one of  claims 36  to  38 ,  
     
     
         40 . A heat shield comprising a graphitic body, formed by a method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder,  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         41 . A heat spreader comprising a graphitic body, formed by a method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         42 . Molten metal contacting apparatus comprising a graphitic body, formed by a method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         43 . Molten metal contacting apparatus as claimed in  claim 42 , in which the apparatus is or comprises a crucible.  
     
     
         44 . Molten metal contacting apparatus as claimed in  claim 42 , in which the apparatus is or comprises a liner, for a crucible or other molten metal contacting apparatus.  
     
     
         45 . An electrode comprising a graphitic body, formed by a method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder, and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         46 . A composite sheet comprising a porous core and a graphitic sheet coating, the graphitic sheet coating being formed by the method comprising the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder, and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         47 . A composite sheet as claimed in  claim 46 , comprising a felt of graphitic material secured between sheets of graphitic material.  
     
     
         48 . A composite sheet as claimed in  claim 46 , comprising a corrugated sheet of graphitic material secured between sheets of graphitic material.  
     
     
         49 . A composite sheet, as claimed in any of  claims 46  to  48 , in which the porous core is secured between the sheets of graphitic material prior to heat treatment of the sheets of graphitic material.  
     
     
         50 . A composite sheet, as claimed in  claim 49 , in which the porous core is rolled between said extruded shapes prior to forming the bodies.  
     
     
         51 . A composite sheet comprising a mesh of metal or plastics fully or partially embedded in a matrix of graphitic material produced by the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder, and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         52 . A precursor for use in the manufacture of silicon carbide by silicising, comprising a body of graphitic material produced by the steps of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         53 . A silicon carbide article produced by silicising a precursor as claimed in  claim 52 .  
     
     
         54 . A graphite body having a coating of a secondary phase, formed by the process of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder,  
 ii) a binder; and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape;  
 d) incorporating said secondary phase into the surface of the extruded shape either before or after forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure.  
 
     
     
         55 . A graphite body having a coating of a secondary phase, as claimed in  claim 54 , in which the secondary phase is or includes silicon carbide.  
     
     
         56 . A graphite body having a coating of a secondary phase, as claimed in  claim 54 , in which the secondary phase is or includes silicon nitride or boron nitride.  
     
     
         57 . A graphite body comprising a temporary secondary phase, formed by the process of:—
 a) forming under high shear a mouldable composition comprising:—
 i) graphite powder;  
 ii) a binder, and  
 iii) an aqueous fluid carrier  
 
 b) working said mouldable composition under high shear to form an extruded shape;  
 c) forming bodies from said shape; and  
 d) heat treating said bodies to stabilise the structure  
 in which said secondary phase is incorporated into the bodies either before heat treatment.